1. Field of Invention
The present invention relates to a method for processing a digital image, and more particularly to a noise suppression method for a digital image.
2. Related Art
Along with the rapid development of digital cameras, demands for digital images are also boosting. The digital camera captures an image frame by using a planar photosensitive element, or retrieves a square area from the image. Once an exposure action is finished, a control circuit transfers charges on a capacitor unit to a next adjacent unit. When reaching the last unit at the edge, the charge signal is transmitted to an amplifier and converted into a potential thereby. The above process is repeated until the whole image frame is converted into potentials, and the potentials are then sampled, digitalized, and stored into a memory.
However, after a long time of exposure of the photosensitive element, fluctuation may occur to surface charges of the photosensitive element. Due to the charge fluctuation, noises are generated in the imaging of the digital image. In addition to the exposure time, the light-receiving capability of the photosensitive element is also enhanced by increasing the gain of the photosensitive element. However, in such a manner, the fluctuation may be more easily resulted to the charges.
The noises are not only generated in hardware processing, but also in software processing. For example, when an edge sharpening process is performed on the digital image, for color pixels originally having non-obvious differences in the digital image, the color gradation between different colors is enhanced due to the sharpening effect. In this manner, particles having different colors may appear in the digital image.
Therefore, in order to improve the quality of the digital image, many camera manufacturers or image processing manufacturers have proposed a variety of denoising methods. In most of the denoising methods, a digital filter technology is generally employed to perform a denoising action. For example, the denoising action may be performed by means of close color correction or blurring. All the above methods can reduce the noises in the digital image, but affect the imaging quality of the whole digital image. For example, in a blurred digital image, although the consistency between the pixels having close colors is enhanced, the original profile borders in the digital image also become fuzzy accordingly.